Is the color asymmetry real, or an artifact of lighting? It looks like different materials on either side of Whim.

The color assymetry is certainly real. The purple hues in the false color pancam composites have been frequently observed in the Burns formation, and have often been commented on in the science team's publications. The cyan colors seem to be typical of Meridiani "soils" rich in blueberries. I think fred's right. The cyan colored sediments are mantling the purple-hued rocks on the left side of that panorama.

Think I've *finally* got the colour balance right(ish) on the Whim Creek pan - that (insert expletive here) green gravel on the left is now grey-blue, at last... ...

Stu: Your images are always beautiful, but I really have to ask why would you want to remove color information from an image if that information reflected real differences in the rocks on Mars?

I understand that we amateurs have to work with uncalibrated images that may not always portray the true, spectral variances of Martian rocks, but if anything comes through on those uncalibrated images, it would probably be the spectral differences. As a scientist, I am always looking for ways to enhance the color differences, which is why I normally prefer to look at the false color imagery. I can understand trying to simulate true colors for the aesthetic human eye, but I think there is a balance where we should not discard useful information.

Actually that's a mistake - since they are uncalibrated the one thing you can't rely on is the apparent spectral differences. Only with the PDS data that we get six months later do you have something you can rely on.

The asymetry (in false color) is evident. The physical cause seems to be a concentration of Burnes Formation hematite concretions on the Easterly side while the West seems pretty much Shoemaker eroded sediments.

The side-to-side difference is presumably real, but the exact spectral characteristics of each side can't be determined from the data we have now. I might be wrong, because I don't do anything with multispectral data, but I thought the images as released to us were subjected to an unquantified contrast stretch.

But, I have generated many images based on brightness ratios which appear very similar in their calibrated and uncalibrated versions.

Phil's correct about the stretching - that makes it impossible to do accurate, quantitative spectroscopy.

But in practice, if the contrast and colour (spectrum) of the various targets are similar (which is probably often the case), then the relative exposures and stretching applied to the different filter frames will be similar. So I'd expect you could get some qualitative spectral information from ratios of the filter frames, at least as far as comparing frame ratios at different sites/targets.

Stu: Your images are always beautiful, but I really have to ask why would you want to remove color information from an image if that information reflected real differences in the rocks on Mars?

Thanks

re the colours... just speaking personally, I am trying to produce as "realistic"* as possible a view of Mars, to share with people who read my blog(s) and who come to my Outreach talks. I can appreciate the usefulness of 'false colour' or even just stretched colour images, and find them useful *personally* for trying to figure out what I'm seeing in the landscape in terms of processes and differences in geology, but the average person who comes to my talks would be confused to hell and back if I showed Mars in an unfamiliar hue. So, again, personally, what I try to do most of all is try to get my colour images to look like the ones seen on the official NASA Pancam site. I very rarely manage that, because of the limits of my own equipment, software and skill, but I have fun doing it, and now and again, usually some time after midnight, at the end of a long work day, an image pops up on my monitor after a lot of work that makes me smile and think "Yeah, that's not bad... I like that..."

* ...which in itself is very subjective, I know. Let's not prise open that can of Barsoomian worms!

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